The present invention relates to a gas turbine system of the type in which an air/fuel mixture is reacted in a catalytic combustor.
Gas turbine systems have been previously proposed in which an air/fuel mixture is compressed by a compressor, and then reacted in a catalytic combustor. For example, U.S. Pat. No. 4,754,607 describes a self-contained energy center or cogeneration system which converts chemical energy into mechanical, electrical, and heat energy. The fuel, preferably a gaseous fuel such as natural gas, is mixed with air in a mixer, and then the resulting mixture enters the compressor. The compressor compresses the air/fuel mixture and outputs the compressed mixture to the cold side of a heat exchanger in which the mixture becomes heated. The heated, high-pressure mixture is then delivered to the combustion chamber of a catalytic combustor. The resulting products of combustion are directed to the inlet of an expansion turbine mounted on the compressor shaft. After powering the turbine, the hot combustion gases are directed through the hot side of the heat exchanger, whereupon those gases supply the heat which is transferred to the cooler air/fuel mixture passing through the cold side of the heat exchanger. The still moderately hot combustion gases exiting the hot side of the heat exchanger are delivered to heat-utilizing devices such as a water heater. Meanwhile, the turbine also drives an electric generator mounted on the compressor shaft for producing electric power.
The use of a catalytic combustor offers the advantage that all of the fuel can be oxidized therein, resulting in ultra low NO.sub.x emissions and low CO and UHC (unburned hydrocarbon) levels. However, that requires that the volume of the catalytic combustor be relatively large, which can be rather costly since a substantial portion of the catalyst is exposed to, and must be designed to withstand, temperatures that are very near the turbine inlet temperature (e.g., around 1600.degree. F. or higher).
Therefore, it would be desirable to provide a system in which the total catalytic combustor volume is large enough to oxidize substantially all of the fuel, while minimizing the percentage of the volume which needs to be able to withstand temperatures as high as the turbine inlet temperature.